Congress needs to set up an independent body that can invoke the 25th
The 25th Amendment allows Congress to designate a body instead of the Cabinet to invoke the 25th. Its clear we cannot count on the Cabinet with the news that some are resigning rather than making the tough decision. It would still require the VP, but we can at least do something.
Whenever the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of the office as Acting President.
It should be a bipartisan commission 5 Democrats and 5 Republicans plus two lawyers, a medical doctor, and some sort of mental health expert. The question is who should appoint them? And how long are their terms?